U.S. Patent Publication No. 2008/0119989 A1 describes a device for preventing a child from being inadvertently left behind in a vehicle. The system of this publication includes an electronic system and a sensor at the child seat. Depending on whether the engine of the vehicle is running or not, a check is performed at regular intervals to ascertain whether a child is sitting in the child seat. As soon as it has been determined that a child has been sitting in the child seat for longer than a predetermined period of time with the engine turned off, an alarm is triggered and, if necessary, a signal is sent to a custodian.